1. Field of the Invention
The present invention relates generally to a bactericidal or bacteriostatic method using cellulose acetate.
2. Related Background Art
Conventionally, inorganic antibacterial agents such as a silver compound or organic antibacterial agents containing an organic compound have been utilized as antibacterial agents used for sterilization or bacteriostasis. In addition, photocatalysts such as titanium oxide, etc. produce active oxygen by photoirradiation. This active oxygen provides an antibacterial action. Hence, titanium oxide or the like also may be used as antibacterial agents.
However, there has been a problem that conventional antibacterial agents have short lives. Accordingly, even when, for instance, resin products using such conventional antibacterial agents exhibit an antibacterial action at the beginning of use, various bacteria propagate or molds (fungi) grow after a certain period of time. Furthermore, conventional antibacterial agents include those that cannot provide effective sterilization or bacteriostatic actions against pathogenic bacteria including, for example, serious alimentary intoxication bacteria such as enteropathogenic Escherichia coli O-157 and methicillin resistant Staphylococcus aureus (MRSA). Even if the conventional antibacterial agents are effective for such bacteria, some of them may have harmful effects on human bodies. In order to provide a resin product or the like with an antibacterial property by using a conventional antibacterial agent, it has been necessary to add and knead the conventional antibacterial agent as an additive. When a sufficient antibacterial property is intended to be provided, it has been necessary to add and knead a large amount of antibacterial agent. This causes a disadvantage in cost and also affects the characteristics of the resin product. On the other hand, the photocatalysts do not allow an antibacterial action to be expressed without the help of light. Therefore, the use of such photocatalysts may be limited in some cases. Moreover, many of the conventional antibacterial agents are expensive and thus their use may be limited in view of their cost.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a safe, simple, and inexpensive method enabling excellent long-term sterilization or bacteriostasis.
In order to achieve the above-mentioned object, the present invention is directed to a method in which cellulose acetate is used for sterilization or bacteriostasis.
The present inventor examined the antibacterial ability of natural organic substances to obtain an antibacterial substance that can solve all the aforementioned problems. As a result, he found out that cellulose acetate had excellent bactericidal and bacteriostatic ability. A particularly remarkable point is that the cellulose acetate exhibits an excellent bactericidal property even against the enteropathogenic Escherichia coli O-157, MRSA, and Trichophyton. The bactericidal or bacteriostatic property of the cellulose acetate remains as long as the cellulose acetate is present and accordingly, lasts for a long period. In addition, since the cellulose acetate is one type of resin, the cellulose acetate itself can be used for a resin product. Even when the cellulose acetate is mixed with other resins, there is a lower possibility that the cellulose acetate may affect the characteristics of the other resins, as compared to the case of conventional antibacterial agents. Moreover, the cellulose acetate is less expensive than the conventional antibacterial agents, is derived from a natural product, and has no safety problem, which has been proved by actual use over a long period.
It is not clear why the cellulose acetate exhibits the bactericidal or bacteriostatic property. However, the present inventor assumes that acetyl groups in the cellulose acetate cause the bactericidal property or the like to be expressed. In the following description, the term xe2x80x9cantibacterialxe2x80x9d includes the meanings of both xe2x80x9csterilizationxe2x80x9d and xe2x80x9cbacteriostasisxe2x80x9d.
Preferably, the cellulose acetate used in the method of the present invention includes acetyl groups in a ratio of 1 to 3 per glucose residue, particularly preferably, in a ratio of 2.5 per glucose residue on average.
In the method of the present invention, preferably, the cellulose acetate is used together with boric acid. According to the knowledge that the present inventor has acquired, the cellulose acetate has an excellent antibacterial property against, for example, alimentary intoxication bacteria or pathogenic bacteria but is decomposed by Bacillus subtilis. This denotes that the cellulose acetate has a biodegradation property. This can be an advantage but also may be a disadvantage depending on the intended use. Hence, when the antibacterial action of the cellulose acetate is intended to be exhibited for a longer period of time, it is preferable that the cellulose acetate and boric acid (an antibacterial agent against the Bacillus subtilis) be used together as described above. The ratio of boric acid to be added to the cellulose acetate is, for example, 100 ppm to 1000 ppm, preferably 200 ppm to 600 ppm, and further preferably 200 ppm to 300 ppm.
In the method of the present invention, the form of cellulose acetate to be used is not particularly limited. For example, the cellulose acetate may be used as an additive agent (an antibacterial agent) or may be processed into a plastic molded article, a coating material, a spray agent, or a textile product.
When used as an antibacterial agent, the cellulose acetate generally is present in a granular form. The grain size of such cellulose acetate is, for example, 0.001 to 5 mm, preferably, 0.001 to 2 mm, and further preferably 0.001 to 0.5 mm. The antibacterial agent may contain components other than the cellulose acetate, for example, a plasticizer such as phthalic acid. The granular antibacterial agent can be produced by, for example, a method including mixing a plasticizer (such as phthalic acid) with cellulose acetate (fine powder), kneading and extruding the mixture in a strand form with a twin screw extruder, and cutting it with a cutter. The mass ratio between the cellulose acetate and the plasticizer is as follows: for example, cellulose acetate:plasticizer=80:20.
Examples of items for which the cellulose acetate antibacterial agent can be used include resin products, coating materials, and textile products. When these products are produced, the antibacterial agent may be mixed with their main raw materials. Products thus obtained are provided with an excellent antibacterial property.
Next, in the method of the present invention, the cellulose acetate can be processed to form a plastic molded article. In this case, preferably, another resin is blended with the cellulose acetate depending on the intended use. Examples of another resin to be blended include thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, fluororesin, acrylic resin, methacrylic resin, polyvinyl acetate, polyamide, acetal resin, polycarbonate, polyphenylene oxide, polyester (polyethylene terephthalate, polybutylene terephthalate, aromatic polyester, polyallylate, etc.), polysulfone-based resin, and polyimide. Besides such thermoplastic resins, a thermosetting resin may be blended. Examples of such a thermosetting resin include phenolic resin, melamine resin, alkyd resin, unsaturated polyester resin, silicone resin, epoxy resin, urea resin, and urethane resin. The plastic molded article can be in a form of, for example, sheet, film, or rod, but is not particularly limited thereto. The ratio of the cellulose acetate in the plastic molded article is, for example, 1 to 100 mass %, preferably 10 to 100 mass %, and further preferably 30 to 100 mass %. For example, the methods of the examples described later can be used for processing the cellulose acetate into a plastic molded article.
Such a plastic molded article can be used variously depending on the intended use. For instance, in the case of a sheet- or film-like plastic molded article, such a plastic molded article may be allowed to adhere to the surface of another product as a protective material, so that the surface can be provided with an antibacterial property. A film made of cellulose acetate may be allowed to adhere to the surface of a product such as, for example, toilet articles, kitchen utensils, medical supplies, bath articles, or the like.
Next, in the method of the present invention, a coating material is prepared with cellulose acetate, and sterilization or bacteriostasis can be achieved using the coating material. Examples of a solvent used in the coating material include ethyl acetate, acetone, and chloroform. It also is preferable to blend an alcohol such as ethanol or methyl alcohol as a dissolution accelerator. This coating material can be manufactured through dissolution of cellulose acetate in a solvent. An example of the composition of this coating material is shown below. In the following composition, a total ratio of the respective components is 100 mass %.
In the above-mentioned composition, preferably, the alcohol component is a mixed alcohol of ethanol and methyl alcohol. In this case, the weight ratio is as follows: for example, ethanol:methyl alcohol=90 to 100:10 to 0, preferably, 90 to 98:10 to 2, and more preferably 98 to 99:2 to 1. The use of ethanol allows a cellulose acetate coating film to be formed having excellent performance. This coating material may contain components other than the cellulose acetate and solvent. Such other components include, for example, pigment or dye.
When the coating material is applied to an object to be treated and then is dried, a coating film of cellulose acetate is formed and exhibits an antibacterial action. The antibacterial action lasts as long as this coating film is present. The method of applying the coating material is not particularly limited, and may be, for example, a brush application method, a method using a roll coater, or a dipping method. The object to be coated also is not limited, and may be, for example, toilet articles, kitchen utensils, medical supplies, bath articles, wallpaper, an inner side of a bathroom, joints between tiles in a bathroom or the like, passageways, closets, chests of drawers, or inner shelves of shoe cupboards or the like.
In the method of the present invention, a spray agent is prepared with cellulose acetate, and sterilization or bacteriostasis can be achieved using the spray agent. The spray agent can be produced by a method including preparing a coating material through dissolution of cellulose acetate in a solvent and filling a can with the coating material together with aerosol. The aforementioned solvents also can be used in this case. Examples of the aerosol include nitrogen gas, LPG, and DME. The blending ratio of the aerosol differs depending on the intended use, but is as follows: for example, coating material:spray gas=70 to 40%:30 to 60%. The method of filling a spray can with the spray agent is a conventional method and the pressure used therein is, for example, 0.3 to 0.5 MPa. In the method of using the spray agent, it is only necessary to blow it on the object to be treated. When the solvent is dried, a cellulose acetate coating film is formed and exhibits the antibacterial action. Examples of the object to be treated are the same as in the case of using the coating material.
Next, in the method of the present invention, cellulose acetate is processed to form fibers, and sterilization or bacteriostasis can be achieved using the fibers. In this case, such fibers may be formed of cellulose acetate alone like acetate fibers, or may be formed of a mixture of cellulose acetate and another resin. When a textile product is manufactured, fibers made of cellulose acetate may be mixed with other fibers and the mixed fibers may be used for the manufacture. The size of the fibers is not particularly limited.
When being formed of cellulose acetate alone, fibers can be manufactured using cellulose, for example, in the same manner as in the case of acetate fibers or triacetate fibers. Initially, the cellulose is esterified with acetic anhydride. Then, the cellulose thus esterified is hydrolyzed partially to have an esterification degree of 55 to 60%, which then is dissolved in acetone. This is spun by a dry spinning method and thus acetate fibers can be obtained. Furthermore, cellulose is esterified with acetic anhydride and thereby triacetate is obtained. This is dissolved in a mixed solvent of methylene chloride and methyl alcohol, which then is spun by the dry spinning method. Thus, triacetate fibers can be obtained.
Fibers made of cellulose acetate can be used for various applications. Application examples follow:
general clothing
lining of European clothes and Japanese clothes (kimonos)
bedding such as bedsheets, pillow cases, pyjamas
underwear, insoles of shoes, etc.
diapers, sanitary goods
towels, bath towels, handkerchieves, dish towels, small towels to be served to guests in a wet state at table, etc.
inner bottom covers for chests of drawer, closets or the like, suit covers
curtains, carpets, center rugs, covers for electric carpets, covers for cushions, covers for xe2x80x9ckotatsu (a Japanese foot warmer with a quilt over it)xe2x80x9d coverlets, tablecloths, luncheon mats
filter sheets of purifiers for city water
respirators, dressings, cloth portions of first-aid bandages or eye bandages
handles of bags or suitcases, covers for leather goods
containers for keeping small articles such as cosmetics (accessory cases)
dust-proof covers (for example, covers for electric fans, toasters, rice cookers, etc.)
The whole or part of each textile product mentioned above may be formed of fibers made of cellulose acetate. For instance, since the cellulose acetate gives an excellent antibacterial action against Trichophyton, the whole sock may be formed of cellulose acetate fibers or only a portion thereof coming into contact with toes may be formed of the cellulose acetate fibers and the other portion may be formed of, for example, nylon fibers with high strength.